Capital Stock - Additional Information (Details) (USD $) In Thousands, except Share data, unless otherwise specified	0 Months Ended	12 Months Ended		0 Months Ended
	Mar. 30, 2012	Dec. 31, 2014	Dec. 31, 2013	Aug. 27, 2012	Jun. 18, 2013	Aug. 16, 2012	Dec. 31, 2012
Class Of Stock [Line Items]
Increased number of authorized preferred stock		25,000,000	25,000,000			10,000,000
7.625% Series A Cumulative Redeemable Preferred stock, par value		$ 0.001	$ 0.001			$ 0.001
Series A preferred stock dividend rate per year		7.625%	7.625%
Total liquidation preference value		$ 287,500	$ 287,500
Issuance of Common stock, offering price	$ 26.81
Issuance of common stock net proceed	539,327
Common stock available for sale		200,000,000	200,000,000
Common stock share authorized to repurchase		7,414,553			10,000,000
Stock repurchased during period, shares		100,000	2,485,447
Stock repurchased during period, value		1,912	43,881
2012 Program
Class Of Stock [Line Items]
Common stock available for sale							10,000,000
Common Stock
Class Of Stock [Line Items]
Issuance of Common stock, shares	20,125,000
Stock repurchased during period, value			2
Common Stock | Over-Allotment Option
Class Of Stock [Line Items]
Issuance of Common stock, shares	2,625,000
Redeemable Preferred Stock
Class Of Stock [Line Items]
7.625% Series A Cumulative Redeemable Preferred stock, par value				$ 0.001
Issuance of Common stock, shares				11,500,000
Shares issued pursuant to full exercise of underwriters' over allotment option				1,500,000
Liquidation preference per share				$ 25.00
Series A preferred stock dividend rate per year				7.625%
Annual dividend per share on the preferred stock				$ 1.90625
Total liquidation preference value				$ 287,500
Series A preferred stock, redemption date				Aug. 27, 2017